Re: Number of low eccentricity distant planets

"Gene Hatch" <spammenot@[EMAIL PROTECTED]
> wrote in message 
news:47C24D14.90000@[EMAIL PROTECTED]
| Erik Max Francis wrote:
| > Crown-Horned Snorkack wrote:
| >
| >> Hot jupiters are easier to detect than the more distant planets like
| >> Solar System giants. However, some planets on long period orbits have
| >> been found.
| >>
| >> Planets on circular orbits, like in Solar System, should be no harder
| >> to find than planets on eccentric orbits. Yet most planetary systems
| >> have eccentric orbits.
| >>
| >> How rare are systems with low eccentricity orbits like Solar System -
| >> excluding the hot jupiters?
| >
| > We don't know yet.  We're still collecting data.
| >
|
|
| Sadly, my math seems to be rusting away, and I don't know If it was ever
| good enough to figure this. My intuition, though, makes me think that a
| planet with a highly eccentric orbit would be easier to detect (using
| stellar doppler shift) than one with a circular orbit of similar period.
| Am I full of crap?
|
| -- Gene the lurker

On the premise that a car travelling at 100 mph is "easier to detect"
than one travelling at 65 mph, yes. A good cop should be able
to detect both, though, since the speed limit in this zone is 25 mph.
What the cop cannot do is measure the speed of a car crossing
a T-junction ahead of him - the equivalent of a face-on orbit.

So -- for a face-on orbit, the position of the star betrays its
planets, but position is very difficult to resolve and there
is no doppler along the line-of-sight.
For an edge-on orbit, doppler along the line of sight
betrays the star's velocity and that betrays the planets.
If the orbit is eccentric and the major axis is along the LOS
then you have maximum doppler and the star approaches
and recedes, but if the major axis crosses the LOS then
you get very little doppler.